The primary objective is the understanding of dynamic processes involving bile salts. There are two principal goals. First, we will study rates of cholesterol crystal growth in model bile solutions as a function of degree of saturation, pH, ionic strength, and polyelectrolyte concentration. This will suggest when gallstone formation can be accelerated or inhibited. Second, we will measure solubilization rates of fatty acids and monoglycerides by bile salt micelles to determine the chemical mechanism involved. By combining our results with earlier studies of triglyceride hydrolysis, we can predict the overall rate of fat solubilization and thus improve our understanding of the kinetics of digestion. Achieving these goals requires physical chemical information about mixed bile salt micelles, to be obtained from measurements of conductance, diffusion, electrophoresis, and density. Since bile salt and fatty acids can diffuse by two parallel routes, we especially want to combine diaphragm cell and Laser-Doppler diffusion measurements. We also plan to study transport through small (less then 25 A) well-defined pores. We plan to check the Onsager reciprocal relations commonly postulated for membrane transport. We will also study the selectivity of these pores coated with silanes with terminal functional groups.